A case study of the sensitivity of numerical simulation of mesoscale convective systems to varying initial conditions.

Abstract

A 12 h nested-grid numerical simulation of a warm-season mesoscale convective weather system (Zhang and Fritsch, 1986) is utilized as a control run in order to 1) test the sensitivity of the numerical simulation to different types of initial conditions; 2) examine the need for an observing system that would resolve mesoscale features; and 3) determine which meteorological variables need to be most carefully considered in observing system design and preprocessing analysis. It is found that improved observational capabilities are likely to have an important impact on the successful prediction of the timing and location of summertime mesoscale convective weather systems if mesoscale features can be resolved. It is also found that procedures to account for the effects of convective systems that are in progress at the time of initialization can make significant contributions to the prediction of the evolution of the meteorological events and to the improvement of the quantitative precipitation forecasts. For summertime situations where the large-scale gradients are weak, detailed temperature and moisture fields appear to be more important than the detailed wind fields in determining the development and evolution of deep convection. However, poor resolution of the wind field such that wind speed magnitudes and gradients are underestimated tends to reduce the degree of mesoscale organization.-from Authors